Brent, meanwhile, was “still having difficulty gaining independent bullish traction,” said Jim Ritterbusch, president of Ritterbusch and Associates in a note.

“Increased Saudi crude availability that is being enhanced by reduced OSPs (official selling prices) into Europe and other regions is providing a strong counter against curtailed Libyan export activities,” Ritterbusch wrote.

In addition to reducing the price of its August barrels, Saudi Arabia also told the Organization of the Petroleum Exporting Countries (OPEC) that it increased production by almost 500,000 barrels per day last month.

Output cuts by OPEC and allies since January 2017 have reduced a crude glut.

Involuntary drops in supply in Venezuela, Angola and Libya have made the cutbacks even bigger, although OPEC - led by Saudi Arabia - has since agreed to a modest increase in output.

“The more that Saudi Arabia adds to the market, the less of a supply cushion we have - that’s a bullish twist to a bearish development,” said Yawger at Mizuho.

An imminent shift in global oil trade flows was also affecting prices.

U.S. tariffs on $34 billion in Chinese imports took effect as a deadline passed on Friday and Beijing has vowed to respond in kind.

China has indicated that it could place a tariff of 25 percent on U.S. oil. If that happens, “Chinese demand would then shift to other suppliers. Because the oil market is already in tight supply due to the numerous outages, this would drive international prices (Brent) further up,” Commerzbank said in a note.

Renewed U.S. sanctions on Iranian oil appear set to tighten supplies further.

South Korea, a major buyer of Iranian oil, will not lift any Iranian crude and condensate in July for the first time since August 2012, three sources familiar with the matter said.

Meanwhile, the market continued to watch rising U.S. crude output, with this week’s oil drilling rig count data, an indicator of future production, due at 1 p.m.

Additional reporting by Alex Lawler in LONDON, Henning Gloystein in SINGAPORE and Meng Meng in BEIJING; Editing by Marguerita Choy and Jan Harvey